Hybrid powertrain architectures comprise torque-generative devices, including internal combustion engines and electric machines, which transmit torque through a transmission device to a vehicle driveline. A hybrid powertrain architecture reduces fuel consumption through the engine by shutting off the engine at opportune moments during ongoing vehicle operation, including events such as the vehicle stopped at a light or in traffic, or when the vehicle is operating on a downhill portion of a highway. A powertrain architecture includes, e.g., an engine and transmission system controlled and mechanized to shut off the engine, and restart it using a belt drive through an alternator, often referred to as a belt-alternator-starter (BAS) device. Other powertrain architectures include engine and transmission systems wherein one or more electrical motors generate motive torque which is transmitted to the vehicle driveline directly or through the transmission.
One such transmission includes a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving motive torque from a prime mover power source, typically an internal combustion engine, and an output member for delivering motive torque from the transmission to the vehicle driveline. Electrical machines, operatively connected to an electrical energy storage device, comprise motor/generators operable to generate motive torque for input to the transmission, independently of torque input from the internal combustion engine. The electrical machines are further operable to transform vehicle kinetic energy, transmitted through the vehicle driveline, to electrical energy potential that is storable in the electrical energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the powertrain system, including controlling transmission gear shifting, controlling the torque-generative devices, and regulating the electrical power interchange between the electrical energy storage device and the electrical machines.
The exemplary electro-mechanical transmissions are selectively operative in fixed gear modes and continuously variable modes through actuation of the torque-transfer clutches, typically employing a hydraulic circuit to effect clutch actuation, including fixed gear modes and continuously variable modes. Engineers implementing powertrain systems having electro-mechanical transmissions are tasked with implementing control schemes to monitor system states and control operation of various systems and actuators to effectively control powertrain operation.
Operation of the powertrain system includes selectively starting and stopping operation of the internal combustion engine. Engine starting can be operator-initiated, wherein the vehicle operator starts the engine by way of a key-on and crank action. Engine starting further comprises automatic engine restarting events during ongoing vehicle operation, wherein the engine is automatically started by the control system. This can be in response to an operator action, such as an accelerator pedal tip-in, or, in response to a control system determination of a need to start the engine and referred to as a quiescent auto-start event. The control system selectively starts and stops operation of the internal combustion engine to optimize energy efficiency, and for other reasons.
During a restart event, compression torque pulses are generated in individual engine cylinders and transmitted to a transmission torque damper and the engine block, which may result in objectionable vibrations reaching the vehicle operator, especially at resonant frequencies for the powertrain and various driveline components. Furthermore, the compression torque pulses can disturb engine output torque and can result in objectionable audible noise. The magnitude of the vibration can be sufficiently great enough to overwhelm feedback damping control systems.
Some current systems for damping engine compression pulses include feed-forward control systems, which attempt to predict the magnitude of the disturbance and provide pre-emptive corrective actions. These systems include engine models that pre-calibrate compression torque disturbances off-line. Such a system requires a minimal amount of real-time computation, but can have poor accuracy, due to variations in real-time operating conditions that affect compression pressures including atmospheric pressure, engine speed profile, and initial engine crank angle.
Therefore, there is a need for a control scheme which effectively addresses vibrations caused during starting of an internal combustion engine, including an engine that is an element of a powertrain system having an electro-mechanical transmission and electrical machines. Such a system is described hereinafter.